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Old 15-03-2009, 11:16   #31
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Originally Posted by Christian Van H View Post
The only question for me now is; since our engine block MUST be grounded to AC and DC ground systems, should I include a conductive strap across my vibration isolating coupler to also ground the propeller shaft and prop?
Why do you have to ground your AC to the engine???
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Old 15-03-2009, 11:17   #32
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Thinwater, where do you find, and what exactly is "Scottish Ice"?
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Old 15-03-2009, 11:49   #33
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However, I have heard of lightening blowing through the transformer, and that was my point. Blows through most things, I gather...
Yes it does, but TRANSFORMERS are CURRENT LIMMITING DEVICES, which may substantially reduce the fault current (as it blows up).

Transformer Fault (let through) Currents:
Impedance is the total current limiting factor ( I = E ÷ Z) ). For transformers it is more convenient to rate the impedance as a percentage than use its absolute value. This is the percentage of normal rated primary voltage, that must be applied to the transformer, to cause full-load rated current to flow in the short-circuited secondary. Typical transformer impedance is between 2% and 9%.

For example, with 5 KVA Transformer @ 120VAC, and an Impedance (Z) of 5%:
Full load current (FLA) = (5 Kva x 1000) ÷ 120 = 41.66 Amps
Short Circuit Current (Isc) = FLA ÷ % Z = 41.66 ÷ 0.05 = 833.33 Amps *

* Ohm's Law:
In a given electrical circuit, the amount of current in Amperes (I) is equal to the pressure in Volts (V) divided by the resistance , in Ohms (R) [or Impedance "Z"], as can be calculated by the by three different iterations of the formula:
To find Current: I = V ÷ R (as above, FLA = V ÷ Z)
To find Voltage: V = I x R
To find Resistance: R = V ÷ I
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Old 15-03-2009, 17:05   #34
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Why do you have to ground your AC to the engine???
Hey Celestial! Here's the link posted earlier: Grounding

Check out the DC and AC sections... I believe you'll find it "Common"!

BTW, I wont use plastic thru's for the same reasons. Anything that comes loose can deliver a death blow to a plastic fitting...NOTHING is gonna take out a bronze seacock, except CORROSION!
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Old 15-03-2009, 17:44   #35
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Originally Posted by Christian Van H View Post
Hey Celestial! Here's the link posted earlier: Grounding

Check out the DC and AC sections... I believe you'll find it "Common"!

BTW, I wont use plastic thru's for the same reasons. Anything that comes loose can deliver a death blow to a plastic fitting...NOTHING is gonna take out a bronze seacock, except CORROSION!
Something come loose on a sailboat??? I've never heard of that before...

I disagree about the AC green ground wire to the engine block You now have a direct path for stray currents from shore to corrode prop shaft and prop. I tie all the AC grounds on the AC outlets of the boat to a common ground buss bar. Then from the power cord receptacle on the boat to the buss bar. Therefore the engine is isolated and protected by the shaft zinc and or internal zinc.
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Old 15-03-2009, 17:51   #36
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You guys don't get it or are using valves instead of flange mount seacocks. You can even use a plastic thru-hull with bronze seacock. There's no fitting to hit with someting that broke off as the thru-hull is completely enclosed by the seacock.

Also, I would rather have a 20 year old plastic thru-hull than a 20 year old bronze thru-hull!

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Old 15-03-2009, 17:51   #37
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You guys don't get it or are using valves instead of flange mount seacocks. You can even use a plastic thru-hull with bronze seacock. There's no fitting to hit with someting that broke off as the thru-hull is completely enclosed by the seacock.

Also, I would rather have a 20 year old plastic thru-hull than a 20 year old bronze thru-hull!

cheers,
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Old 15-03-2009, 17:54   #38
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You guys don't get it or are using valves instead of flange mount seacocks. You can even use a plastic thru-hull with bronze seacock. There's no fitting to hit with someting that broke off as the thru-hull is completely enclosed by the seacock.

Also, I would rather have a 20 year old plastic thru-hull than a 20 year old bronze thru-hull!

cheers,
Nick.
Now you sound like my ex-wife Nick...But honey...I do get it...The bronze tri-plate valve totally encompasses the plastic thru-hull...but...I DON'T LIKE PLASTIC UNDER THE WATER!!!
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Old 15-03-2009, 18:17   #39
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Celestial ;-) So how about your boat? I understand it must be metal not plastic like polyester, and you weld the seacocks on without using PU sealant and other plastic stuff like that??!!

cheers,
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Old 15-03-2009, 18:17   #40
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Celestial ;-) So how about your boat? I understand it must be metal not plastic like polyester, and you weld the seacocks on without using PU sealant and other plastic stuff like that??!!

cheers,
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Old 15-03-2009, 18:25   #41
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Oh Nick stop!!! You know my boat is F/G. I just like what I've done for years. F/G boat, bronze thru-hulls, bronze valves, no bonding, no BS.
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Old 15-03-2009, 19:07   #42
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I disagree about the AC green ground wire to the engine block You now have a direct path for stray currents from shore to corrode prop shaft and prop.
Dont forget my Galvanic isolator, my friend!
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Old 16-03-2009, 02:02   #43
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To add some perspective to the bonding of bronze (or any other metal) through hulls; this was originally done on timber vessels to protect the TIMBER around the through hull rather than the metal of the through hull.

The circuit was two (slightly) dissimilar metals, the seawater AND the damp timber. The current through the timber destroyed the celluar structure of the timber. By bonding the through hulls, the current flowed through the much lower resistance of the bonding wire rather than the damp timbers.

With nonconductive hulls (F/G, F/C, Epoxied timber etc), there doesn't seem to be any need to bond the through hulls IMO.
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Old 16-03-2009, 10:08   #44
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If a boat has an inboard engine. This provides a path of least resistance to ground. At least it should be sufficient. On boats with outboards, I imagine bonding might offer some benefit.

On lightning protection. This is almost like a "which anchor is best" subject. I think a separate thread consisting of folks who have been struck while onboard might be interesting, As opposed to reiterating what we've all read.

I for one would love to compare notes.
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Old 16-03-2009, 10:52   #45
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If a boat has an inboard engine. This provides a path of least resistance to ground.
For any normal charge that travels solely through wiring, that is true. But lightning doesn't play to those rules.

I imagine myself as being the lightning: I'm up there and want to go to ground down there and I travel fast as lightning (ha!). I am powerful, I can even make air conductive by ionizing it but will only do that if needed. Any (more or less) conductive object between me and my goal can help me as I can travel through that more easily. I look down and see that nice aluminium pole on that floating thingy and select that as part of my route. I jump into it and travel downward to it's base, saving my strength by not having to ionize air. The electrical current I cause is normal for lightning, somewhere between 20,000 and 200,000 amps. I see some wires in that mast but they melt/evaporate mostly so my main charge is still in the mast as I reach it's base. Hmmm.... they did not provide me with a nice conducting path from here so I have to decide what to do. Ground is my target and it's close, some fiberglass and a couple of feet of air (catamaran) and I'm there. I also see that engine further aft with it's nice conducting shaft into ground, so I have to decide:

Let's travel down, the fibreglass is easy and I ionize a couple feet of air (nothing compared to the many thousands of feet I did before reaching this pole) and I'm home. I probably left a hole in that fiberglass.

Or shall I make that turn to horizontal, which doesn't really bring me closer to earth but towards that engine? That turn is difficult for me traveling at this speed and if there's more air to travel through, I would be better off continuing down but that human body in between me and the engine looks nice and moist so I use that and anything else in the way to jump to and find my way to ground without leaving holes in the fiberglass.

A good thick (AWG 6 or bigger) conductor connected to the mast base, going straight (no bends) down to earth will always be the path selected when a lightning strike travels down the mast, making you the one who decides the route.

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